The application of a permanent magnet has extended to a wide range of fields, such as electronics, information and communication, medical treatment, machine tool, and industrial and automotive motors. In addition, with a growing demand for reduction in carbon dioxide emissions, expectations for development of a permanent magnet with higher properties are recently increasing in terms of, e.g., widespread use of hybrid cars, energy saving in the industrial field, and enhancement of power generation efficiency.
An Nd—Fe—B-based magnet dominating the market at present as a high-performance magnet is recently expanding its application to an automobile, an elevator, a component for wind-power generation, etc. from the application to a voice coil motor (VCM) and a nuclear-magnetic resonance imaging system (MRI) at an early stage of development.
With respect to the motor that is a principal application of a permanent magnet, an Nd—Fe—B-based magnet is used for motors having a wide range of output powers from several W to several kW. Among these motors, an automotive motor is used in an environment at a high temperature of a hundred and several tens of ° C., and the motor itself generates heat due to high-load rotation. Accordingly, a magnet used in an automotive motor is required to reduce deterioration of the magnetic properties at a high temperature.
As to the Nd—Fe—B-based magnet, magnetization and coercivity are easily deteriorated due to an increase in the temperature of the magnet. In order to ensure magnetic properties, particularly, coercivity of the Nd—Fe—B-based magnet at a high temperature, Dy is often added to an Nd—Fe—B-based magnet. However, since Dy is produced in limited areas, the element is not easily ensured in recent years, and the price thereof also starts rising.
For this reason, instead of an Nd—Fe—B-based magnet, studies are being made on a rare earth magnet excellent in the magnetic properties at a high temperature.
For example, Patent Document 1 discloses a rare earth magnet having a main phase with an ThMn12-type crystal structure and a non-magnetic grain boundary phase such as SmCu4, SmFe2Si2 and ZrB.